The present invention relates to a reflection-type liquid crystal display device, more specifically, to a reflection-type color liquid crystal display device containing a color filter therein, capable of displaying in multiple colors.
As a conventional reflection-type liquid crystal display device, a reflection-type liquid crystal display device of a monochrome display using a TN (twisted nematic) liquid crystal cell or an STN (super twisted nematic) liquid crystal cell, is mainly used.
For the growing demand of displaying in colors in recent years, however, reflection-type color liquid crystal display devices containing color filters therein have been vigorously developed.
The reflection-type liquid crystal display devices containing color filters therein are broadly classified into the following three types.
The first type is a reflection-type color liquid crystal display device using no polarizing films. There are several devices belonging to this type, one using Guest-Host liquid crystal in which a dichroic pigment or a black dye is mixed in a liquid crystal material to fill a liquid crystal cell with, another using polymer-dispersion liquid crystal in which a liquid crystal material is dispersed in a polymer, and so on. Since any one of them does not use a polarizing film, it is excellent in brightness but low in contrast, and thus it has not been realized for practical use yet.
The second type is a reflection-type color liquid crystal display device having a color filter provided in a liquid crystal cell of a typical monochrome liquid crystal display device using two polarizing films.
Since this type uses two polarizing films, it is excellent in contrast, but it has a disadvantage of a dark display as well as a problem that its chroma is not good because of occurrence of color mixture caused by a reflective layer provided outside its glass substrate.
The third type is a reflection-type color liquid crystal display device using one polarizing film and containing a reflective layer inside a liquid crystal cell.
This reflection-type color liquid crystal display device is excellent in chroma with little color mixture because light is reflected by an inner surface of the liquid crystal cell. Accordingly, the liquid crystal display devices of this type have been vigorously developed.
Hereinafter, the structure of the reflection-type color liquid crystal display device of this type will be briefly explained using FIG. 7. FIG. 7 is a schematic sectional view showing a part of the conventional reflection-type color liquid crystal display device considerably enlarged.
In this liquid crystal display device, a reflective layer 103 is first formed on a first substrate 101 which is a transparent glass substrate, and a color filter 104 composed of three color filters of red (R), green (G) and blue (B) is formed thereon. Further, a protective film 105 is formed on the color filter 104, and many first electrodes 106 in a stripe-shape are formed thereon. The first electrodes 106 are extended to form row side wiring patterns 126 and row side input patterns 128 simultaneously.
On the other hand, many second electrodes 107 in a stripe-shape are formed on the lower surface of the second substrate 102 which is a transparent glass substrate. The second electrodes 107 are extended to form column side wiring patterns (not shown) and column side input patterns (not shown) simultaneously.
The first substrate 101 and the second substrate 102 are opposed such that the first electrodes 106 and the second electrodes 107 are perpendicular to each other, and coupled to have a predetermined gap therebetween with a seal 123. Then, the gap between the two substrates 101 and 102 is filled with liquid crystal to form a liquid crystal layer 108.
Thereby, a liquid crystal cell 100 is constituted in which the (STN) liquid crystal layer 108 is sandwiched between the two transparent substrates 101 and 102.
Both the first electrodes 106 and the second electrodes 107 in the liquid crystal cell 100 are transparent electrodes made of indium tin oxide (ITO), and many electrodes are arranged side by side in directions perpendicular to each other to form pixels at respective intersections thereof. At a position corresponding to each pixel, each color filter of the color filter 104 is arranged in such an order of R, G, and B in both the directions perpendicular to each other.
Further, a row side driving IC 21 and a column side driving IC (not shown) are mounted, as liquid crystal driving ICs which are semiconductor integrated circuit devices (referred to as xe2x80x9cICxe2x80x9d), at desired positions on the first substrate 101 and the second substrate 102 of this liquid crystal cell 100, respectively. This is referred to as a chip-on-glass.
In this event, protruding electrodes (bumps) 21a serving as input/output terminals of the row side driving IC 21 are aligned with and bonded to wires of the row side wiring patterns 126 and the row side input patterns 128 with an anisotropic conductive adhesive 30, and further the each protruding electrode 21a is electrically connected to each wire. As for the not shown column side driving IC, its each protruding electrode is similarly bonded to as well as electrically connected to each wire of the column side wiring patterns and the column side input patterns with an anisotropic conductive adhesive.
Finally, a retardation film 111 and a polarizing film 113 (absorption-type polarizing film) are provided outside the second substrate 102 to complete a liquid crystal display device.
However, the conventional reflection-type color liquid crystal display device configured as above has some problems described below.
First of all, since the reflective layer 103 needs to have a high reflectance, aluminum (Al) or silver (Ag) is used as its material. Both of them, however, have poor chemical resistance.
Therefore, in the case of using aluminum or silver as the reflective layer 103, it is necessary to form a film for protecting aluminum or silver on its top surface. In other words, it is necessary to use aluminum or silver together with the protective film on its top surface as the reflective layer 103.
Typically, a silicon oxide (SiO2) film is formed as the protective film by a sputtering method or a vacuum evaporation method, and further the formation of the aluminum film or the silver film on the first substrate 101 and the formation of the silicon oxide film thereon are sequentially performed in order to prevent the reflectance from decreasing due to oxidation of the surface of the aluminum film or the silver film.
The silicon oxide film has good compatibility with the color filter 104 which is to be formed thereon, and thus the color filter 104 can stably be formed thereon.
However, when silicon oxide exists on aluminum or silver, it is very difficult to pattern the reflective layer 103 because silicon oxide has excellent chemical resistance.
As countermeasures against this problem, it can be considered that the aluminum film or the silver film and the silicon oxide film are formed on the entire surface of the first substrate 101 as the reflective layer 103.
This eliminates the need to pattern the reflective layer 103. This makes it impossible, however, to observe the row side wiring patterns 126 and the row side input patterns 128 from the outside of the first substrate 101 because the reflective layer 103 is opaque.
Further, it is also impossible to observe the row side wiring patterns 126 and the row side input patterns 128 through the row side driving IC 21 because the row side driving IC 21 and the column side driving IC, which are semiconductor integrated circuit devices made of silicon, are opaque.
For this reason, it becomes impossible to align the protruding electrodes 21a on the lower surface of the row side driving IC 21 with the row side wiring patterns 126 and the row side input patterns 128. As a result, accurate electrical connection between the row side driving IC 21 and the row side wiring patterns and the row side input patterns can not be established, which makes it impossible to constitute a liquid crystal display device.
It is an object of the invention to solve these problems and to stably provide a reflection-type color liquid crystal device which is bright and excellent in chroma and has sufficient chemical resistance.
The reflection-type color liquid crystal display device according to the invention is a reflection-type color liquid crystal display device comprising: a liquid crystal cell including an STN liquid crystal layer composed of nematic liquid crystal which is aligned at a twist angle range of 180xc2x0 to 270xc2x0 sandwiched between a transparent first substrate having first electrodes and a transparent second substrate having second electrodes, and provided with a reflective layer on the first substrate, and a color filter of a plurality of colors on at least one of the first and second substrates; a polarizing film provided on a visible side of the second substrate; a retardation film provided between the polarizing film and the second substrate; and a liquid crystal driving integrated circuit for driving the liquid crystal cell, and the reflection-type color liquid crystal display device is configured as follows to attain the aforementioned object.
The second substrate is larger than the first substrate, and the reflective layer is provided on the entire surface of the first substrate. Further, wiring patterns for the first electrodes extending to an area of the second substrate outside an area of the second substrate superposed on the first substrate and input patterns for the liquid crystal driving integrated circuit on the area of the second substrate outside the first substrate, are provided on a surface of the second substrate provided with the second electrodes.
Furthermore, the first substrate and the second substrate are coupled with an anisotropic conductive seal having anisotropy in a direction of electrical conduction, and the first electrodes are electrically connected with the wiring patterns for the first electrodes through the anisotropic conductive seal.
Moreover, the liquid crystal driving integrated circuit is mounted on the second substrate, and input/output terminals of the liquid crystal driving integrated circuit are electrically connected to the wiring patterns and the input patterns through an anisotropic conductive adhesive, respectively.
It is preferable to provide the color filter on the first substrate.
Further, the second substrate is preferably thinner than the first substrate in thickness.
Furthermore, the retardation film may be composed of a twisted retardation film, a first retardation film, and a second retardation film which are sequentially arranged from the second substrate side to the polarizing film side.
In the reflection-type color liquid crystal display device according to the invention, the reflective layer is formed on the entire surface of one of the substrates. Therefore, the reflective layer does not need to be patterned at all.
As a result, the reflective layer having excellent chemical resistance can easily be formed by forming a silicon oxide (SiO2) film having excellent chemical resistance on an aluminum film or a silver film having an excellent reflectance but poor chemical resistance.
Moreover, the two substrates are coupled using the anisotropic conductive seal, which makes it possible that the electrodes on the substrate formed with the reflective layer are electrically connected to wires of the wiring patterns formed on the opposite substrate, and that all the liquid crystal driving ICs for driving the liquid crystal cell are mounted on a substrate without reflective layer.
Since the liquid crystal driving ICs are mounted on the substrate without reflective layer, the opaque reflective layer, even if existing on the entire surface of the substrate, is not an obstacle to alignment of positions of the input/output terminals of the liquid crystal driving ICs and the wiring patterns, which enables the alignment by viewing them from the outside of the substrate without reflective layer.